Reply to "circuit protection"

@PLCProf posted:

I think John is talking about an L-C low-pass arrangement, with the TVS as the C. The supply to the electronics would be taken off across the TVS. So, the L protects the DCS track signal from the shunt capacitance of the TVS, but the TVS is directly across the electronics, affording maximum protection to the electronics, but less protection to the track.

Correct, I'm not trying to protect the track, as Adrian has already pointed out, a TVS at some distance across the track may provide minimal or no protection.

@Adrian! posted:

I think I'm probably confused and not saying the right thing for the thread or didn't write it well. Back to step one...

1. You can't put a choke at the input of a DCS engine since then the PS board gets no signal.

2. You can't put a choke in series with a TVS to protect other electronics, or the TVS is no longer effective at suppressing a voltage across the series combination.

Correct, and I was specific as to the engines I recommended this combination on.

@gunrunnerjohn posted:

As I've frequently said, the absolute best place for the TVS is inside the locomotive directly across the track power feed.  Obviously, this is also the hardest place to install them, and you have to modify every locomotive.  Of course, while you're in there, you can add the 22uh choke in the track power feed for any TMCC/Legacy locomotives to minimize any effect the their electronics on the DCS signals.  If you choose to do that, the best way is to put the choke in the center track feed and then the TVS diode across the feed after the diode.  That way the DCS signal isn't significantly affected by the bulk capacitance of the TVS diode in the locomotive.

This combo was what I envisioned for TMCC/Legacy locomotives.  It serves a two-fold purpose.  Not only does it isolate the track from the stray capacitance of the TVS, but it also addresses the issue of the TMCC/Legacy electronics attenuating the DCS signal.  We know that a number of those locomotives will have a negative effect on the DCS signal, so this checks that box as well.